Electric rheostat



(No Model.) 3 Sheets-Sheet 1.

. P. H. DOANE.

ELECTRIC RHBOSTAT. N 58,36Z. Pate 11 Apr. 14,1896.

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(No Model. 3 Sheets-Sheet 2.

F. H. DOANE. ELEOTRIG RHEOSTAT.

No. 558,362. Patented Apr. 14, 1896.

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P. H. DUANE. ELECTRIC RHEOSTAT. No. 558,362. A Patented Apr 14, 1896.

AN DREW EGRAHAM. PHOTU-UTHQWASHINGTON. DC.

UNITED STATES PATENT OFFICE.

FRANCIS II. DOANE, OF NEIVTON, MASSACHUSETTS, ASSIGNOR TO THE FRANK RIDLON COMPANY, OFSACO, MAINE.

ELECTRIC RHEOSTAT.

SPECIFICATION forming part of Letters Patent No. 558,362, dated April 14, 1896.

Application filed September 30, 1895. Serial No. 564,074. (No model.)

To all whom it may concern:

Be it known that I, FRANCIS II. DOANE, a citizen of the United States, residing at Newton, in the county of Middlesex and State of Massachusetts, have invented certain new and useful Improvements in Rheostats, of which the following is a specification.

- My invention relates to rheostats; and it consists, essentially, in a rheostat having its resistances composed of one or more bars of highly-resisting material arranged and connected as hereinafter more fully described.

My invention is especially adapted for use as a starting-rheostatthat is to say, one which is used for the purpose of starting electric motors by gradually reducing the resistance of the circuit until a desired maximum current through the motor is obtained. I have consequently shown and described a preferred form of my invention as embodied in a starting-rheostat, but I do not consider that the advantages of my device are limited to such a use.

In the accompanying drawings, Figure 1 represents a top plan view of a rheostat embodying my invention. Fig. 2 is an edge view of the same. Fig. 3 is a plan view thereof with the cover removed. Fig. 4 is a central transverse section taken on the line 00 cc of Fig. 1. Fig. 5 is a detail view of a part hereinafter described. Fig. (3 is a diagrammatic view showing the electrical connections of the apparatus. 1

In making my rheostat I prefer to provide a shallow box A, such as shown in the drawings, which may have suitable lugs a wherebyit may be secured to any desired support. Vithin this box I place the resistances which in use are to be introduced into or withdrawn from the circuit. Such resistances have hitherto usually been made of wire, and the main objections to such a material which have arisen are, that, inasmuch as the metal of which the wires are composed is a good conductor of electricity, such wires generally have to be made of great length in order to provide the desired resistance, and are expensive on that account, and they also, by reason of their length, ordinarily make a rheostat heavier and more cumbrous than is desirable. In my invention I have obviated these difficulties by using graphite for the resistances, which material I have found to be especially useful for this purpose for the reason that it has a much greater resistance than any metal, and consequently but little of it need be used to produce a high resistance, while it also possesses the advantages of cheapness and compactness, and does not burn out nor deteriorate, even when heated to a red heat.

I prefer to make my graphite resistances in the form of short bars 2. I have shown a number of these bars held in place in the box A by means of ametallic strip 3, provided with holding-clips 4:, which are clamped around the centers of the graphite bars and thereby firmly hold the same in position, as shown in Fig. The strip 3 is fastened to the bottom of the boX and is insulated therefrom. A convenient way of making electrical connections with the graphite bars 2 is by means of metallic clips 5 clamped around the same, to which suitable connecting-wires (3 are attached. I have shown four of these clips 5 on each bar 2 of graphite. By this means I get four different resistances from each bar, as will presently be explained more fully.

The mechanism for introducing the various resistances is preferably located on the outside of the cover B of the boX A. This cover should be made of some suitable insulating materialsuch, for instance, as slate-and apertures 7 should be left in the ends of the box 13 for the sake of ventilation. On the top of the cover 13, I provide a number of metallic contacts 8, which are arranged in two rows, as shown, the individual contacts being staggered to those opposite, so that they will be successively engaged e11 alternate sides by the slider 9. Each contact piece may consist of a block 9, secured in any suitable manner to the slate top B and provided with a metallic spring arm 10, which bears against the top of the slide 9 when the latter is moved thereunder, and between which and the graphite bars electrical connection is made, as will presently be described. These contact-pieces 8 are insulated from each other by the air-space which exists between them, or, if desired, positive insulating material, such as mica, may be placed. between. them. The slider 9 is guided and at the same time held against the top 13 of the box on which it slides by means of the guides 11, which lap over its beveled edges. II t is provided with an insulated handle 12, whereby it may be moved under the successive contact-pieces 8, thus making electrical connection therewith, until at the limit of its .l'orward movement its front end 13, which is llattened, asshown, engages the metallic contacts H and 11. The slider 9 is preferably provided at its rear end with a rod 15, which passes through. and is guided in abearing 16. This rod has a head 17 at its outer end, between which head and the bearing 16 a coiled spring 15 is arranged, which tends to keep the slider ll in the position shown in Figs. 1 and 2 ol' the drawings.

My preferred method of connecting the various resistances and electrical contacts of my rhcost'at is shown in Fig. (5, in which the contact-pieces 8, the graphite bars, and the connecting-wires are shown diagrammatically, it being understood, of course, that the graphite bars are in reality located beneath the contact-pieces 8, and that the connecting-wires pass through the cover of the box. The lirst contact-piece which is en gaged by the slider l) is connected to the clip 5 on. one extreme end of one of the graphite bars (which one is immaterial) by a wire 20. The second contact-piece to be engaged is connected to one extreme end of anotherbar, or, preferably, to the other extreme end of the same bar by a wire 21. The third contact-piece is connected to an extreme end of another graphite bar by a wire 22, and so on until all the extreme ends of the graphite bars have been connected, as shown. The next connection is made by means of a wire 23 from the next contact-piece to one of the intermediate clips 5. The next contact-piece is connected to another intermediate clip, and so on. It will be seen that for each clip 5 there is a corresponding contactpiece 9, electrieally connected therewith.

The number of graphite bars and the number of clips 5 on each. bar can of course be varied from the specific arrangement shown in the drawings; but in making the connections between the clips and the contact-pieces s the same order must be observed as above (lOSClllJOd-llfllllOlY, the clips on the extreme ends of the graphite bars are to be connected to the contact-pieces which are the first to be engaged by the slider 9, the next adjacent clips to the next group of contact-pieces to be .:ngaged, and so on, the clips nearest the holdiug strip 3 being connected to the last group of contact-pieces. The reason for this arran gement will be apparent when the operation of the device is described.

Two binding-posts 18 and 19 are provided on the cover 13, which in use are connected in the circuit with the motor and the source of energy. It is immaterial at which post the current enters the rheostat.

The metallic strip 3 which holds the graphite bars is electrically connected by a wire 2-1- to one of the binding-posts, as 18, and the same binding-post is also electrically connected to the metallic contact-piece 11-. The other binding-post is connected to the slider 9 by means of a wire 25, attached to the bearing 10, and it is also electrically connected to the contact-piece 11 by a wire 26.

As thus constructed, the operation of my device is as follows: \Vhen the slider t) is thrown back by the spring 15 to its normal position, no current can pass through the device. \Vhcn it is moved forward until it ongages with the nearest contact-piece 8, an electrical connection is established between the binding-posts 18 and 19 by means of the wires 2-1 20, the slider 0, the metallic strip 3, and the graphite bar 2, to which the wire 20 is connected, and the resistance thus introduced into the circuit depends upon the half-length and the diameter of the graphite bar, the resistance of the wires and other parts being negligible in comparison therewith. This represents the greatest resistance which can be thrown into the circuit bymeans of the rheostat, and consequently under such circumstances a minimum current will. llow from one binding-post to the other, the dimensions of the graphite bar being of course calculated, so as to produce the desired1ninimum current. \Vhen the slider is pushed forward until it engages the second contacts piece 8, an additional path for the current is offered through the wire 21 and its graphite bar, and the resistance through this path being equal to the former resistance and the two being joined in multiple are, the total resistance is thereby halved, and consequently twice the current will flow. In the same manner, as the slider is pushed forward, successive half-lengths of graphite are thrown into the circuit in multiple arc and the resistance is thereby successively reduced in correspondin g proportion. lVhen the slider has passed half-way down, it reaches the contaetpiece to which the wire 23 is attached, and as said. wire is connected to its graphite bar 2 at an intermediate point of its length, the resist ance is diminished in proportion to the length.

of the graphite thus cut out and a further increasepf current takes place, and so on, the intermediate clips 5 being successively thrown into the circuit in multiple arc until the slider is in electrical contact with all the contact-pieces 8. Its end 13 may then final] y be pushed under the contact-pieces 11 and 1-1, and as these are connected respectively with the binding-posts 18 and 19 the entire current is allowed to short-circuit through. the slider without passing through any of the graphite resistances. The motor being thus started and supplied with the full current it is desirable that the slider be held with its end 13 in contact with the pieces lit and 14s. To this end 1 have provided a springarm I), secured to the cover 13 and adapted to engage with a notch c in the rod 15 when the slider is moved forward to its short-circuiting position, where it is thus held until released by pressing the spring-arm b upward, when it is thrown entirely out of contact with any of the contact-pieces by means of the spring 15. The advantage of having this spring 15 is that it is thereby rendered impossible for the current to be accidentally left partially turned on.

\Vhile I have described my device as a starting-rheostat, yet it is equally well adapted for use wherever it is desired to introduce a varying resistance into an electrical circuit, and it may obviously be changed in many respects to adapt it to such uses without departing from the spirit of my invention.

I have also described graphite as being my preferred material for the resistances, but bars of other highly-resisting materials, such as are well known in the art, may of course be used instead, and the number of such bars may be varied as desired, and also the number of metallic clips 5 011 each bar. Furthermore, I do not consider myself limited to the precise arrangement shown and described of the terminal connections of the resistances.

I claim-- 1. In a rheostat the combination of a plurality of bars of highly-resisting material, metallic bands secured to the same at suitable intervals of their lengths, a contact-terminal corresponding to each metallic band, said bands being electrically connected each to a contact-tenninal, and the said bars be-. ing also connected through a common metallic strip to the external circuit, and a movable arm completing the connection with the external circuit and arranged to make contact with the said contact-terminals successively, all substantially as described.

2. In a rheostat, the combination of a metallic holding-strip electrically connected.

with a plurality of metallic connections for the purpose set fOrthTeach of the said connections being electrically connected to one of the said contact-terminals, all substantially as described.

In testimony whereof I have hereunto subscribed my name this 24th day of September, 1895.

FRANCIS II. DOANE.

Witnesses:

EVERETT D. CHADWICK, ELLEN TOMLINSON. 

